Method for unsupervised clustering of multimedia data using a large-scale matching system

ABSTRACT

A method and apparatus for unsupervised clustering of a large-scale collection of multimedia data elements. The method comprises generating a first cluster from the large-scale collection by: matching each of the multimedia data elements to all other multimedia data elements in the large-scale collection, determining a clustering score for each match being performed, clustering multimedia data elements having a clustering score above a threshold to create the first cluster; and storing the first cluster in a storage unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patent application Ser. No. 12/507,489 filed Jul. 22, 2009, now allowed, which is a continuation-in-part of the following:

-   -   (1) U.S. patent application Ser. No. 12/084,150 having a filing         date of Apr. 7, 2009, now pending, which is the National Stage         of International Application No. PCT/IL2006/001235, filed on         Oct. 26, 2006, which claims foreign priority from Israeli         Application No. 171577 filed on Oct. 26, 2005 and Israeli         Application No. 173409 filed on 29 Jan. 2006; and     -   (2) U.S. patent application Ser. No. 12/195,863, filed Aug. 21,         2008, now U.S. Pat. No. 8,326,775, which is a         continuation-in-part of the above-referenced U.S. patent         application Ser. No. 12/084,150, and which also claims priority         under 35 USC 119 from Israeli Application No. 185414, filed on         Aug. 21, 2007.

All of the applications referenced above are herein incorporated by reference.

TECHNICAL FIELD

The invention relates clustering of multimedia data elements, compressing the clusters and matching new content to these clusters.

BACKGROUND

With the abundance of multimedia data made available through various means in general and the Internet and world-wide web (WWW) in particular, there is also a need to provide for effective ways of searching for such multimedia data. Searching for multimedia data in general and video data in particular may be challenging at best due to the huge amount of information that needs to be checked. Moreover, when it is necessary to find a specific content of video, the prior art cases revert to various metadata that describes the content of the multimedia data. However, such content may be complex by nature and not necessarily adequately documented as metadata.

The rapidly increasing multimedia databases, accessible for example through the Internet, calls for the application of effective means for search-by-content. Searching for multimedia in general and for video data in particular is challenging due to the huge amount of information that has to be classified. Prior art techniques revert to model-based methods to define and/or describe multimedia data. However, by its very nature, the structure of such multimedia data may be too complex to be adequately represented by means of metadata. The difficulty arises in cases where the target sought for multimedia data is not adequately defined in words, or respective metadata of the multimedia data. For example, it may be desirable to locate a car of a particular model in a large database of video clips or segments. In some cases the model of the car would be part of the metadata but in many cases it would not. Moreover, the car may be at angles different from the angles of a specific photograph of the car that is available as a search item. Similarly, if a piece of music, as in a sequence of notes, is to be found, it is not necessarily the case that in all available content the notes are known in their metadata form, or for that matter, the search pattern may just be a brief audio clip.

A system implementing a computational architecture (hereinafter “The Architecture”) that is based on a PCT patent application number WO 2007/049282 and published on May 3, 2007, entitled “A Computing Device, a System and a Method for Parallel Processing of Data Streams”, assigned to common assignee, and is hereby incorporated by reference for all the useful information it contains. The Architecture consists of a large ensemble of randomly, independently, generated, heterogeneous processing cores, mapping in parallel data-segments onto a high-dimensional space and generating compact signatures for classes of interest.

A vast amount of multimedia content exists today, whether available on the web or on private networks. Grouping efficiently such multimedia content into groups, or clusters, is a daunting assignment that requires having appropriate metadata for the clustering purposes, or having it done manually by identifying commonalities for the clustering purposes. Difficulties arise when portions of multimedia content are not readily recognized for the purpose of clustering. For example, if a picture of the Lincoln Memorial in the sunset is not tagged as such, then only a manual search will enable to cluster this image with other pictures of sunsets.

Therefore, it would be advantageous to provide a solution for unsupervised clustering of multimedia content that would cure the deficiencies of prior art techniques.

SUMMARY

Certain embodiments disclosed herein include a method for unsupervised clustering of a large-scale collection of multimedia data elements. The method comprises generating a first cluster from the large-scale collection by: matching each of the multimedia data elements to all other multimedia data elements in the large-scale collection, determining a clustering score for each match being performed, clustering multimedia data elements having a clustering score above a threshold to create the first cluster; and storing the first cluster in a storage unit.

Certain embodiments disclosed herein also include an apparatus for unsupervised clustering of a large-scale collection of multimedia data elements. The apparatus comprises at least one processing unit; a storage unit for storing one or more clusters of multimedia data elements; a memory coupled to the at least one processing unit, of which at least a portion of the memory contains instructions that when executed by the at least one processing unit configure the apparatus to: generate a first cluster from the large-scale collection by: matching each of the multimedia data elements to all other multimedia data elements in the large-scale collection, determining a clustering score for each match being performed, clustering multimedia data elements having a clustering score above a threshold to create the first cluster; and storing the first cluster in the storage unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram showing the basic flow of The System for large-scale multimedia matching.

FIG. 2 is a diagram showing the flow of patches generation, response vector generation, and signature generation in a Large-Scale Speech-to-Text System implemented in accordance with certain embodiments of the invention.

FIG. 3 is a flowchart of a method for unsupervised clustering based on a signature matching using The Architecture.

FIG. 4 is a diagonal matrix showing the matches found between multimedia data elements.

FIG. 5 is a diagonal matrix showing first level clusters of matched multimedia data elements.

FIG. 6 is a diagonal matrix showing the cumulative match score for the clusters.

FIG. 7 is a diagonal matrix showing a second level of clustering.

DETAILED DESCRIPTION

It is important to note that the embodiments disclosed by the invention are only examples of the many advantageous uses of the innovative teachings herein. In general, statements made in the specification of the present application do not necessarily limit any of the various claimed inventions. Moreover, some statements may apply to some inventive features but not to others. In general, unless otherwise indicated, singular elements may be in plural and vice versa with no loss of generality. In the drawings, like numerals refer to like parts through several views.

A large collection of multimedia data elements calls for clustering of the multimedia data. Accordingly to certain exemplary embodiments of the invention multimedia data elements are clustered in an unsupervised manner. The invention describes a clustering technique which entails one comparison of every one of the multimedia data elements to all other multimedia data elements and determining a comparison score. Based on the score, clustering of the multimedia data elements having a score above a predetermined threshold. The process is then repeated for the clusters as they become larger clusters until a cycle where no more clustering can be achieved. In one embodiment instead of the multimedia data elements, the initial comparison is performed on Signatures unique to the multimedia data elements. The representation in clusters and clusters of clusters enables compression, storage and discovery of new content-related elements by matching to the generated clusters.

In one embodiment, instead of the multimedia data elements that include, but are not limited to, images, audio, video, fragments thereto, and any combination thereof, the initial comparison is performed on Signatures unique to the multimedia data elements. The comparison between all the pairs of the multimedia data elements' signatures yields the Inter-Match Matrix. The clustering is performed on this Inter-Match Matrix which is a sparse matrix. This process results in Clusters of Signatures. It should be noted that the same Signature can be related to more than one element, and several signatures can represent a single element. Thus, the clustering of the Signatures and the representation of the Cluster by a reduced set of signatures, which optimally spans the Cluster, enables reduced storage and effective representation for discovery of new content-elements related to the cluster. For example, a specific combination of the Signatures in the Cluster may lead to match of new content-element, which originally were not part of the set the Cluster was based on. The method can be implemented in any applications which involve large-scale content-based clustering, recognition and classification of multimedia data. These applications include, for example, content-tracking, video filtering, multimedia taxonomy generation, video fingerprinting, speech-to-text, audio classification, object recognition, video search and any other applications that require content-based signatures generation and matching for large content volumes such as, web and other large-scale databases.

Certain embodiments of the invention include a framework, a method, a system and their technological implementations and embodiments, for large-scale matching-based multimedia Deep Content Classification (DCC). The system is based on an implementation of a computational architecture, The Architecture” referenced above. The Architecture consists of a large ensemble of randomly, independently, generated, heterogeneous processing computational cores, mapping in parallel data-segments onto a high-dimensional space and generating compact signatures for classes of interest.

In accordance with certain principles of the invention, a realization of The Architecture embedded in large-scale matching system (hereinafter “The System”) for multimedia DCC may be used. The Architecture receives as an input stream, multimedia content segments, injected in parallel to all computational cores. The computational cores generate compact signatures for the specific content segment, and/or for a certain class of equivalence and interest of content-segments. For large-scale volumes of data, the signatures are stored in a conventional way in a database of size N (where N is an integer number), allowing match between the generated signatures of a certain content-segment and the signatures in the database, in low-cost, in terms of complexity and response time.

For the purpose of explaining the principles of the invention there is now demonstrated an embodiment of The System. Other embodiments are described in the patent applications which of which this patent application is a continuation-in-part of and are specifically incorporated herein by reference. Moreover, it is appreciated that other embodiments will be apparent to one of ordinary skill in the art.

Characteristics and advantages of the System include but are not limited to: The System is flat and generates signatures at an extremely high throughput rate; The System generates robust natural signatures, invariant to various distortions of the signal; The System is highly-scalable for high-volume signatures generation; The System is highly-scalable for matching against large-volumes of signatures; The System generates Robust Signatures for exact-match and/or partial-match with low-cost, in terms of complexity and response time; The System accuracy is scalable versus the number of computational cores, with no degradation effect on the throughput rate of processing; The throughput of The System is scalable with the number of computational threads, and is scalable with the platform for computational cores implementation, such as FPGA, ASIC, etc.; and, the signatures produced by The System are task-independent, thus the process of classification, recognition and clustering can be done independently from the process of signatures generation, in the superior space of the generated signatures.

Large-Scale Video Matching System—The System

The goal of a large-scale video matching system is effectively to find matches between members of large-scale Master DB of video content-segments and a large-scale Target DB of video content-segments. The match between two video content segments should be invariant to a certain set of statistical distortions performed independently on two relevant content-segments. Moreover, the process of matching between a certain content-segment from Master DB to Target DB consisting of N segments, cannot be done by matching directly the Master content-segment to all N Target content-segments, for large-scale N, since such a complexity of O(N), will lead to non-practical response times. Thus, the representation of content-segments by both Robust Signatures and Signatures is critical application-wise. The System embodies, but is not limited to, a specific realization of The Architecture for the purpose of Large-Scale Video Matching System.

A high-level description of the process for large-scale video matching is depicted in FIG. 1. The multimedia content segments (2) from Master and Target databases (6) and (1) are processed in parallel by a large number of independent computational Cores (3) that constitute the Architecture. Further details are provided in the cores generator for Large-Scale Video Matching System section below. The independent Cores (3) generate a Robust Signatures and Signatures (4) for Target content-segments and a Robust Signatures and Signatures for Master content-segments, which are further saved in a Master Robust Signatures and Signatures (5), and Robust Signatures and Signatures (8). An exemplary and non-limiting process of signature generation for an audio component is shown in detail in FIG. 2. Finally, Target Robust Signatures and/or Signatures are effectively matched, by a matching algorithm (9), to Master Robust Signatures and/or Signatures database to find all matches between the two databases.

To demonstrate an example of signature generation process, it is assumed, merely for the sake of simplicity and without limitation on the generality of the invention, that the signatures are based on a single frame, leading to certain simplification of the computational cores generation. This is further described in the cores generator for Large-Scale Video Matching System section. The system is extensible for signatures generation capturing the dynamics in-between the frames.

Signature Generation

The signatures generation process will be described with reference to FIG. 2. The first step in the process of signatures generation from a given speech-segment is to break-down the speech-segment to K (where K is an integer equal to or greater than 1) patches (14) of random length P (where P is an integer equal to or greater than 1) and random position within the speech segment (12). The break-down is performed by the patch generator component (21). The value of K and the other two parameters are determined based on optimization, considering the tradeoff between accuracy rate and the number of fast matches required in the flow process of the System. In the next step, all the K patches are injected in parallel to all L (where L is an integer equal to or greater than 1) computational Cores (3) to generate K response vectors (22). The Signature (4) is generated by the signature generator (23).

Creation of Signature Robust to Statistical Noise

In order to generate Robust Signatures, i.e., Signatures that are robust to additive, Gaussian, or other linear and not non-linear noise L computational cores, generated for Large-Scale Video Matching System are used. A frame i is injected to all the cores. The cores generate two binary response vectors {right arrow over (S)}—the Signature, and {right arrow over (RS)}—Robust Signature.

For generation of signatures robust to additive noise, such White-Gaussian-Noise, scratch, etc., but not robust to distortions, such as crop, shift and rotation, the core C_(i)={n_(i)} may consist of a single (LTU) node or more nodes. The node equations are:

$V_{i} = {\sum\limits_{j}{w_{ij}k_{j}}}$

n_(i)=θ(V_(i)−TH_(x)); θ is a Heaviside step function; w_(ij) coupling node unit (CNU) between node i and image component j (for example, grayscale value of a certain pixel j); k_(j) is an image component j (for example, grayscale value of a certain pixel j); Th_(x) is a constant Threshold value where x is ‘S’ for Signature and ‘RS’ for Robust Signature; and V_(i) is a Coupling Node Value.

The Threshold values Th_(x) are set differently for Signature generation and for Robust Signature generation. For example, for a certain distribution of V_(i) values (for the set of nodes), the thresholds for Signature Th_(S) and Robust Signature Th_(RS) are set apart, after optimization, according to the following criteria:

I: For: V_(i)>Th_(RS) 1−p(V>Th _(S))−1−(1−ε)^(l)<<1

i.e., given that/nodes (cores) constitute a Robust Signature of a certain image I, the probability that not all of these l nodes will belong to the Signature of same, but noisy image, Ĩ is sufficiently low (according to a system's specified accuracy).

II: p(V _(i) >Th _(RS))≈l/L

i.e., approximately/out of the total L nodes can be found to generate Robust Signature according to the above definition.

III: Both Robust Signature and Signature are generated for certain frame i.

It should be understood that the creation of a signature is a unidirectional compression where the characteristics of the compressed data are maintained but the compressed data cannot be reconstructed. Therefore, a signature can be sued for the purpose of comparison to another signature without the need of comparison of the original data. The detailed description of the signature generation is discussed in more detail in the pending patent applications of which this patent application is a continuation-in-part of, and is hereby incorporated by reference.

Computational Cores Generation

Cores Generation is a process of definition, selection and tuning the Architecture parameters for a certain realization in specific system and application. The process is based on several design considerations, such as:

(a) The cores should be designed so as to obtain maximal independence, i.e. the projection from a signal space should generate a maximal pair-wise distance between any two cores' projections in a high-dimensional space.

(b) The cores should be optimally designed for the type of signals, i.e. the cores should be maximally sensitive to the spatio-temporal structure of the injected signal, for example, and in particular, sensitive to local correlations in time and space. Thus, in some cases a core represents a dynamic system, such as in states' space, phase space, edge of chaos, etc., which is uniquely used herein to exploit their maximal computational power.

(c) The cores should be optimally designed with regard to invariance to set of signal distortions, of interest in relevant application.

Unsupervised Clustering

FIG. 3 shows an exemplary and non limiting flowchart 300 describes a method for unsupervised clustering implemented in accordance with an embodiment of the invention. In an exemplary embodiment, the method is based on signature matching that makes use of the Architecture. As noted above a multimedia data element may be a video, a video frame, a video clip, a picture, an audio recording, and other kinds of multimedia data elements, as well as fragments and/or combinations thereof. It should be further noted that the received multimedia data element may also be a portion of a full image, for example, without limitation, a logo that is shown on certain television shows, or a cartoon character used in a movie, and the like, and is not limited to visual images.

In S310, a plurality of multimedia data elements are received. In S320, the multimedia data elements are arranged in a diagonal two-dimensional matrix, as further explained with reference to FIGS. 4 through 7. Initially, each entry in the matrix is a cluster that comprises a single multimedia data element. In S330 signatures are generated in accordance with the principles of signature generation discussed herein above, for each and every of the plurality of multimedia data elements received. The signatures are generated as explained in more detail above, as well as in the co-pending patent applications of which this patent application is a continuation-in-part of. One of the signatures may be a Robust Signature.

In S340 matches are performed between each signature of a cluster in the rows of the matrix and the signatures of the other clusters, and storing the match result value in the appropriate cell of the matrix. This process is further explained in more detail below. It should be noted that a multimedia data element or for that matter, a cluster, is not matched to itself, i.e., a signature is not matched to itself, and in the case of a cluster, two clusters will not be matched if the same element is present in the two clusters being compared. In S350 it is determined whether there is at least a match that is above a predetermined threshold. It should be noted that as the process is an iterative process, that a different threshold value may be used as iterations advance. In S360, if a match is above or equal to a predetermined threshold, then execution continues with S370; otherwise, execution continues with S380 which causes, for example, the storage of the matrix results in a storage, or sending a report to the system of completion of the determination of the unsupervised clustering process. In S370 clusters are formed from the clusters that were determined to be above the predetermined threshold. These new clusters are now arranged in a matrix similar to the initial matrix but containing fewer rows and columns as a result of the clustering process. An exemplary initial cluster is shown in FIG. 4 and an exemplary secondary cluster, comprised of the clusters of clusters is provided, for example, in FIG. 5, and are discussed in more detail below. In one embodiment of the invention signatures are not generated for the multimedia data elements and comparison is performed directly between the multimedia data elements.

One of the advantages of using the signatures for the purpose of the clustering process is the speed in which such comparison can be performed as well as the lesser amount of resources required. Furthermore, the process using signatures is highly scalable and advantageous in the ever increasing amounts of multimedia data elements being made available. It should be further noted, that it is easy to add an additional multimedia data element once the initial matrix was created. When applicable, a signature of the newly added multimedia data element is created. A row and a column are added to the matrix and the clustering process described above is repeated. Similarly, removal of a multimedia data element requires only the removal of the respective row and column of that multimedia data element and repeating the clustering process.

Reference is now made to FIGS. 4 through 7 where exemplary and non-limiting tables of the clustering process in accordance with the invention are shown. In FIG. 4 signature S1 through S9 are matched, at each match a score of the level of the match is provided., For example, it is determined that the score for the match between S1 and S2 is “9” while the score of the match between S5 and S8 is “5”. According to the process, a threshold is now applied to determine which two signatures will be in a cluster. Assuming a threshold value of “4”, then while S3 and S4 will be grouped in a cluster as the score exceeds the threshold, S5 and S6 are not clustered because their score is less than the threshold. A group of seven clusters is therefore identified based on this criteria and these are: {S1,S2}, {S1,S8}, {S3,S4}, {S3,S5}, {S5,S7}, {S5,S8} and {S7,S9}.

FIG. 5 now shows the results of matches between the selected clusters, where no cluster is matched to itself and each matching occurs only once. Furthermore, in accordance with the method two items are not matched if a signature Si (i=1, 2, . . . , 9) is present in both clusters being matched. For example, the clusters {S1,S2} and {S1,S8} are not matched as the signature S1 appears in both. This is denoted by an “X” to show that no matching is made. Where matches take place the score from the table shown in FIG. 4 is entered, so in each entry there will be four score values. For example, in the entry for the pair {S1,S2} and {S3,S4} the values “0,0,0,0” are entered, while for {S1,S2} and {S5,S8} the values “1,1,13,1” are entered.

FIG. 6 now shows the cumulative score result where the scores entered into each entry are summed up, therefore, for the pairs {S1,S2} and {S3,S4} the score is “0” while for the pairs {S1,S2} and {S5,S8} the score is “16”. The clustering process may now continue for another iteration. Assuming a threshold value of “8”, i.e., only clusters that have a score of 8 or more may be clustered, it can be seen that only four new clusters can be achieved: {S1,S2,S5,S8} having a score of “16”, {S1,S8,S5,S7} having a score of “8”, {S3, S5,S7,S9} having a score of “17” and {S5,S8, S7,S9} also having a score of “17”. Now the process of a 4×4 matrix takes place and shown in FIG. 7. As can be seen in all combinations there is a repeat of at least one signature in two clusters that are to be matched as in this case no score is determined all locations are marked with an “X”. However, in other examples it is possible that this would not have occurred. In such a case the score would have been determined and checked against the prevailing threshold for that iteration. The process ceases once it is not possible any more to create new clusters which will happen once a single cluster is created, or it is not possible to have any more matches, or otherwise, the match is found to be below a defined threshold value.

The unsupervised clustering process maps a certain content-universe onto a hierarchical structure of clusters. The content-elements of the content-universe are mapped to signatures, when applicable. The signatures of all the content-elements are matched to each other, and consequently generate the inter-match matrix. The described clustering process leads to a set of clusters. According to one embodiment of the invention, each cluster is represented by a small/compressed number of signatures, for example signatures generated by The Architecture as further explained hereinabove, which can be increased by variants. This structure results in a highly compressed representation of the content-universe.

In one embodiment of the invention a connection graph between the multimedia data elements of a cluster may be stored. The graph can then be used to assist a user searching for data to move along the graph in the search of a desired multimedia data element. In another embodiment, upon determination of a cluster, a signature for the whole cluster may be generated based on the signatures of the multimedia data elements that belong to the cluster. It should be appreciated that using a Bloom filter may be used to reach such signatures. Furthermore, as the signatures in accordance with the principles of the disclosed invention are correlated to some extent, the hash functions of the Bloom filter may be replace by simpler pattern detectors, with the Bloom filter being the upper limit.

While signatures are used here as the basic data elements, it should be realized that other data elements may be clustered using the principles of the invention. For example, a system generating data items is used, where the data items generated may be clustered according to the disclosed principles. Such data elements may be, without limitation, multimedia data elements. The clustering process may be performed by dedicated hardware or using a computing device having storage to store the data elements generated by the system and then performing the process described herein above. Then, the clusters can be stored in memory for use as may be deemed necessary.

Moreover, the principles of the invention are implemented as hardware, firmware, software or any combination thereof. Moreover, the software is preferably implemented as an application program tangibly embodied on a program storage unit or computer readable medium. The application program may be uploaded to, and executed by, a machine comprising any suitable architecture. Preferably, the machine is implemented on a computer platform having hardware such as one or more central processing units (“CPUs”), a memory, and input/output interfaces. The computer platform may also include an operating system and microinstruction code. The various processes and functions described herein may be either part of the microinstruction code or part of the application program, or any combination thereof, which may be executed by a CPU, whether or not such computer or processor is explicitly shown. In addition, various other peripheral units may be connected to the computer platform such as an additional data storage unit and a printing unit.

All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. 

What is claimed is:
 1. A method for unsupervised clustering of a large-scale collection of multimedia data elements, comprising: generating a first cluster from the large-scale collection by: matching each of the multimedia data elements to all other multimedia data elements in the large-scale collection, determining a clustering score for each match being performed, clustering multimedia data elements having a clustering score above a threshold to create the first cluster; wherein the generation of the first cluster includes generating for each of the multimedia data elements at least one respective signature, and performing the clustering on the respective generated signatures, thereby the created clusters include a collection of signatures respective of the multimedia data elements, wherein a signature is generated from multiple patches of a multimedia data element, wherein multiple patches are of random length and random position within the multimedia data element; and storing the first cluster in a storage unit.
 2. The method of claim 1, further comprising: repeating the generation of a new cluster from the first cluster and un-clustered multimedia elements in the large-scale data collection until a single cluster is reached, wherein a different threshold value is used for generation of each new cluster.
 3. The method of claim 1, further comprising: stopping the generation of the new cluster when it is determined that a single cluster cannot be reached.
 4. The method of claim 2, wherein repeating the generation of the new cluster further comprising: generating a N-th cluster from previously generated clusters, wherein N is any integer number greater than one.
 5. The method of claim 4, wherein generation of the N-th cluster further comprises: clustering each of the previously generated clusters to all other previously generated clusters; determining a clustering score for each match being performed; clustering multimedia data elements in clusters having a clustering score above the threshold to create the N-th cluster; and storing the N-th cluster in the storage unit.
 6. The method of claim 5, wherein the clustering score is below the threshold if two clusters of the previously generated clusters include at least one overlapping multimedia data element or a multimedia data element is matched to itself.
 7. The method of claim 1, wherein the single cluster cannot be reached when no two multimedia data elements have a clustering score above the threshold or when no two previously clustered elements have a clustering score above the threshold.
 8. The method of claim 1, wherein each of the multimedia data elements is at least one of: audio, image, video, a video frame, fragment of audio, fragment of image, fragment of video, a fragment of a video frame, and an image of a signal.
 9. The method of claim 8, wherein the image of a signal is at least one of: a medical signal, a geophysical signal, a subsonic signal, a supersonic signal, an electromagnetic signal, and an infrared signal.
 10. The method of claim 1, wherein each signature is generated by a plurality of computational cores enabled to receive a plurality of multimedia data elements, each computational core having properties independent from other of the computational cores, wherein each computational core generates responsive to a multimedia data element a respective first signature element and a respective second signature element, the first signature element being a robust signature.
 11. The method of claim 10, further comprising: setting the properties of each of the plurality of computational cores to have at least some statistical independency from other of the plurality of computational cores, the properties being set independently of each other core.
 12. The method of claim 9, wherein generating the respective signature further comprising: applying a Bloom filter on signatures of multimedia data elements in a cluster of the multimedia data elements.
 13. The method of claim 12, wherein applying the Bloom filter comprising: detecting a pattern of the signatures of multimedia data elements of the cluster.
 14. A computer software product embedded in a non-transient computer readable medium containing instructions that when executed on the computer perform the method of claim
 1. 15. An apparatus for unsupervised clustering of a large-scale collection of multimedia data elements, comprising: at least one processing unit; a storage unit for storing one or more clusters of multimedia data elements; a memory coupled to the at least one processing unit, of which at least a portion of the memory contains instructions that when executed by the at least one processing unit configure the apparatus to: generate a first cluster from the large-scale collection by: matching each of the multimedia data elements to all other multimedia data elements in the large-scale collection, determining a clustering score for each match being performed, clustering multimedia data elements having a clustering score above a threshold to create the first cluster; wherein the generation of the first cluster includes generating for each of the multimedia data elements at least one respective signature and performing the clustering on the respective generated signatures, thereby the created clusters include a collection of signatures respective of the multimedia data elements, wherein a signature is generated from multiple patches of a multimedia data element, wherein multiple patches are of random length and random position within the multimedia data element; and storing the first cluster in the storage unit.
 16. The apparatus of claim 15, wherein the processing unit is further configured to: repeat the generation of a new cluster from the first cluster and un-clustered multimedia elements in the large-scale collection until a single cluster is reached or until it is determined that a single cluster cannot be reached, wherein a different threshold value is used for generation of each new cluster.
 17. The apparatus of claim 16, wherein the processing unit is further configured to: generate a N-th cluster from previously generated clusters, wherein N is any integer number greater than one.
 18. The apparatus of claim 17, wherein the processing unit is further configured to generate the N-th cluster by: clustering each of the previously generated clusters to all other previously generated clusters; determining a clustering score for each match being performed; clustering multimedia data elements in clusters having a clustering score above the threshold to create the N-th cluster; and storing the N-th cluster in the storage unit.
 19. The apparatus of claim 18, wherein the clustering score is below the threshold if two clusters of the previously generated clusters include at least one overlapping multimedia data element or a multimedia data element is matched to itself.
 20. The apparatus of claim 15, wherein each of the multimedia data elements is at least one of: audio, image, video, a video frame, fragment of audio, fragment of image, fragment of video, a fragment of a video frame, and an image of a signal.
 21. The apparatus of claim 20, wherein the image of a signal is at least one of: a medical signal, a geophysical signal, a subsonic signal, a supersonic signal, an electromagnetic signal, and an infrared signal.
 22. The apparatus of claim 15, wherein the processing unit includes a plurality of computational cores enabled to receive a plurality of multimedia data elements, each computational core having properties independent from other of the computational cores, wherein each computational core generates responsive to a multimedia data element a respective first signature element and a respective second signature element, the first signature element being a robust signature. 